(A) Field of the Invention
This invention relates to noise simulators, and, in particular, to improvements in such noise simulators wherein a simulated high-frequency pulse noise is reliably fed to electric equipment being tested without reflection.
(B) Prior Art
A noise simulator for feeding a high-frequency noise pulse to electrical equipment, such as data processors is disclosed in "Noise simulators help find peril in power-line defects" described by Mr. M. L. Tandon in Electronics, Mar. 7, 1966, pp. 117-121. Especially, in the drawing in page 120 in this article, a simulator for high-frequency transients simulation operates disclosed which is on the principle of a charged delay line. According to the description of the drawing, "a length of coaxial line (50.OMEGA. coaxial cable) is charged to a given voltage. The mercury-wetted relay R.sub.1 is closed, initiating a pulse which travels in the direction of the one-megohm resistor. The resistor appears as an open circuit to the pulse, 100% reflection occurs, and the pulse travels back to the output of the coaxial line and is dissipated in the terminating 50-ohm resistor. A voltage appears across this impedance for the time it takes for the pulse to travel the length of the coaxial line and back. The amplitude of the pulse generated is one half that of the voltage to which the coaxial line has been charged. This pulse is coupled to the equipment by the three 0.1 microfarad capacitors C. A filter isolates the noise pulse to eliminate the possibility of interference with equipment not being tested."
Although a pulse can be generated in the simulator and injected onto the power line of the tested equipment, I found that the pulse waveform applied to the tested equipment changed in dependence on the input impedance of the equipment, as shown in FIGS. 1a and 1b. In certain input impedances of equipment, a vibratory wave is applied to the equipment as clearly shown in FIG. 1a. It is understood that this is caused by the existence of reflection due to the impedance mismatching. In this connection, the impedance matching is not established in the simulator of the above described literature.
On the other hand, since various types of equipment are tested by use of a noise simulator and since different equipment has different input impedance, it is difficult to establish impedance matching with various types of equipment.